This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this background section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
In a synchronized TDD system, adjacent carrier frequencies or carriers close to each other in the frequency domain are frame synchronized (i.e., have same or almost the same frame start timings) and use the same TDD configuration (i.e., same UL/DL/special subframe configuration). In an unsynchronized TDD system, adjacent carrier frequencies or carriers close to each other in the frequency domain can use different TDD configuration and/or can have any frame start timings. For ease of reference, “adjacent carriers” will be used herein to refer to adjacent carrier frequencies and/or carriers close to each other in the frequency domain.
Adjacent carriers may belong to different operators. To mitigate interfering with each other, operators may choose to synchronize their TDD operations. This means that the operators must generally agree on the TDD configuration to be used on the adjacent carriers. One disadvantage of the synchronized TDD is that the operators may be prevented from choosing a TDD configuration that may be more suitable to each operator's traffic demand.
Operators can choose to operate using unsynchronized TDD so that each operator can choose its own TDD configuration on its carrier. This means that the frames of the adjacent carriers can be misaligned and the TDD configuration can be different. This can lead to significant interference issues. BS-to-BS (base station to base station) interference can thus be of particular concern.
To mitigate such interference issues in unsynchronized TDD, a sufficient guard band (e.g., 5 MHz) is generally required between the unsynchronized carriers. This leads to a waste of spectrum which could otherwise be used to carry traffic. This can also lead to requiring a vendor to implement operator specific RF components (e.g., RF filters, power amplifiers, etc) for each unsynchronized carrier frequency.
In some countries, regulators are also assigning the unused spectrum (e.g., guard bands) for some other operation or technology including non-cellular technologies. These auxiliary operations may lead to further challenges with respect to coexistence issues. A particular problem is observed in some countries where regulators do not adopt common allocation of spectrum, sizes of guard bands, and/or restricted blocks.
Restricted blocks are used in Europe where such frequency blocks are highly restricted in the allowed level of operational power or unwanted emissions. This may further accentuate the need for BS equipment that is capable of meeting radio related regulatory requirements under the constraint of different allocation and different level of inter-operator guard band and/or restricted block. Customized solutions to address particular challenges in different regions may in turn increase the cost, effort and complexity of the equipment, apart from the wastage of the spectrum in form of guard band/restricted blocks.
A frequency band or an operating frequency band supports a specific duplex mode of operation. The possible duplex modes are:                FDD—frequency division duplex:                    Used in e.g., UTRAN FDD and E-UTRAN FDD;            UL (uplink) and DL (downlink) transmissions take place on different paired carrier frequency channels;            UL and DL transmissions can occur simultaneously in time;                        TDD—time division duplex:                    Used in e.g., UTRAN TDD and E-UTRAN TDD;            UL and DL transmissions take place on same carrier frequency channel in different time slots or subframes;                        HD-FDD—half duplex FDD (can be regarded as a hybrid scheme):                    Used in e.g., GSM, GPRS, GERAN, EDGE;            Like FDD mode, UL and DL transmissions take place on different paired carrier frequency channels;            Unlike FDD mode, UL and DL transmissions do not occur simultaneously in time;            Like TDD mode, UL and DL transmissions can take place in different time slots or subframes.                        
There is also another special case of FDD band called “downlink FDD band” (aka DL FDD only band). A well known example is that of LTE (Long Term Evolution) DL FDD band (717-728 MHz), which is being standardized. It does not have UL part of the spectrum. Therefore, for UL transmission the DL FDD band is always used in carrier aggregation mode with another FDD or TDD band such as LTE FDD band 2.
LTE (Long Term Evolution) operates in different duplex modes including FDD, TDD and half duplex FDD. LTE TDD uses unpaired spectrum, which is similar to other TDD systems such as UTRA TDD and TD-SDMA. In LTE, DL and UL transmission are based on radio frames of 10 ms duration. There are two radio frame structures—type 1 for FDD and type 2 for TDD. Type 2 frame structure is applicable to LTE TDD system [see e.g. reference 1 ], and is illustrated in FIG. 1, which illustrates the time domain radio frame structure.
Each 10 ms radio frame consists of two 5 ms half-frames, and each half-frame consists of five 1 ms subframes. Each subframe is one of a DL subframe, a UL subframe or a special subframe (or simply S subframe). Each subframe can be further subdivided. As seen, each UL and DL subframe is divided into two slots, each of 0.5 ms duration. The S subframe is divided into fields DwPTS (downlink pilot time slot), GP (guard period), and UpPTS (uplink pilot time slot). The sum durations of DwPTS, GP, and UpPTS is equal to 1 ms. Different combinations of DL, UL, and S subframes give rise to different TDD configurations.
The supported UL-DL configurations in LTE TDD are listed in Table 1, where for each subframe of the radio frame, “D” denotes that the subframe is reserved for DL transmissions, “U” denotes that the subframe is reserved for UL transmissions and “S” denotes a special subframe. As seen, UL-DL configurations with both 5 ms and 10 ms DL-to-UL switch-point periodicity are supported. In case of 5 ms periodicity, the S subframe exists in both half-frames. In case of 10 ms periodicity, the S subframe exists in the first half-frame only.
TABLE 1LTE TDD UL-DL configurationsDownlink-Uplink-to-UplinkdownlinkSwitch-pointSubframe numberconfigurationperiodicity0 1 234 5678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD65 msDSUUUDSUUD
Regarding the S subframe, the durations of DwPTS and UpPTS are given in Table 2, and are subject to a condition that the total duration of DwPTS, GP and UpPTS is equal to 1 ms.
TABLE 2LTE TDD special subframe configuration (lengths of DwPTs/GP/UpPTS)Normal cyclic prefix Extended cyclic prefix in downlinkin downlinkUpPTSUpPTSSpecialNormalExtendedNormalExtendedsub-cycliccycliccycliccyclicframeprefix prefix prefixprefix configu-ininin inrationDwPTSuplinkuplinkDwPTSuplinkuplink0 6592•Ts 7680•Ts119760•Ts20480•Ts2192•Ts2560•Ts221952•Ts2192•Ts2560•Ts23040•Ts324144•Ts25600•Ts426336•Ts 7680•Ts5 6592•Ts20480•Ts4384•Ts5120•Ts619760•Ts4384•Ts5120•Ts23040•Ts721952•Ts—824144•Ts—
Subframes 0 and 5 and DwPTS are always reserved for DL transmissions. UpPTS and the subframe immediately following the S subframe is always reserved for UL transmission. This means subframe 2 is always reserved for UL. For the 5 ms periodicity, subframe 7 is also reserved for UL. Subframes 3, 4, 8, 9, may be reserved for either UL or DL. For 10 ms DL-to-UL switch point periodicity, subframe 7 may also be reserved for either UL or DL.
In a TDD cell, the TDD configuration is characterized by UL-DL-S subframe configuration. In this disclosure, the term “TDD configuration” used hereinafter refers to a combination of UL-DL configuration (e.g., one of in Table 1) and S subframe configuration (e.g., one of in Table 2) configured in the TDD cell.
The subject matter is not limited to the configurations listed in Tables 1 and 2. Also, the subject matter is not limited to TDD configuration—one or more aspects are applicable to other configurations including FDD, HD-FDD, DL FDD band, among others.
In TDD mode, the radio transceiver in the UE and in the radio node (e.g., base station) switches between the receiver and the transmitter for receiving and transmitting the radio signals. The change in the direction from DL to UL and vice versa is commonly called as RX/TX (or TX/RX) switching.
The requirements related to the TX (transmitter)/RX (receiver) switching are predefined for both UE and BS. For LTE base station, the 3GPP specification TS 36.104 [i.e. reference 7] indicates that the durations of DL and UL transient periods are 17 μs. The transient periods define time periods during which the DL and UL subframes change states from the OFF to ON periods and vice versa [see for example reference 7]. The DL/UL/DL transient period for the LTE TDD base station is illustrated in FIG. 2. In practice, the transceivers are likely to transient periods shorter than 17 μs for both transitions from OFF to ON and from ON to OFF.
New frequency bands for different technologies are being standardized with an ever increasing pace. Various internal and regional regulatory organizations and standardization bodies are also expending considerable effort in introducing these bands to be widely used to facilitate roaming, to simplify device implementation, and to reduce costs. Due to the increasing demand for mobile services coupled with scarcity of spectrum (e.g., scarcity of spectrum below 1 GHz range is a particular concern) efficient use of the available spectrum is becoming particularly important.
Standard bodies such as 3GPP are specifying frequency bands and associated aspects including frequency band number (aka band indicator), channel arrangement, signaling and requirements for different bands. These standardized principles and requirements can potentially be used in different countries or regions. They enable the mobile terminal and network manufacturers to build products according to the need and market demands in different parts of the world.
TABLE 3E-UTRA operating bandsUplink (UL) Downlink (DL) E-UTRAoperating band BS operating band BS Operatingreceive UE transmittransmit UE receiveDuplexBandFUL_low-FUL_highFDL_low-FDL_highMode1  1920 MHz-1980 MHz  2110 MHz-2170 MHzFDD2  1850 MHz-1910 MHz  1930 MHz-1990 MHzFDD3  1710 MHz-1785 MHz  1805 MHz-1880 MHzFDD4  1710 MHz-1755 MHz  2110 MHz-2155 MHzFDD5  824 MHz-849 MHz  869 MHz-894MHzFDD61  830 MHz-840 MHz  875 MHz-885 MHzFDD7  2500 MHz-2570 MHz  2620 MHz-2690 MHzFDD8  880 MHz-915 MHz  925 MHz-960 MHzFDD91749.9 MHz-1784.9 MHz1844.9 MHz-1879.9 MHzFDD10  1710 MHz-1770 MHz  2110 MHz-2170 MHzFDD111427.9 MHz-1447.9 MHz1475.9 MHz-1495.9 MHzFDD12  699 MHz-716 MHz  729 MHz-746 MHzFDD13  777 MHz-787 MHz  746 MHz-756 MHzFDD14  788 MHz-798 MHz  758 MHz-768 MHzFDD15ReservedReservedFDD16ReservedReservedFDD17  704 MHz-716 MHz  734 MHz-746 MHzFDD18  815 MHz-830 MHz  860 MHz-875 MHzFDD19  830 MHz-845 MHz  875 MHz-890 MHzFDD20  832 MHz-862 MHz  791 MHz-821 MHzFDD211447.9 MHz-1462.9 MHz1495.9 MHz-1510.9 MHzFDD22  3410 MHz-3490 MHz  3510 MHz-3590 MHzFDD23  2000 MHz-2020 MHz  2180 MHz-2200 MHzFDD241626.5 MHz-1660.5 MHz  1525 MHz-1559 MHzFDD25  1850 MHz-1915 MHz  1930 MHz-1995 MHzFDD26  814 MHz-849 MHz  859 MHz-894 MHzFDD. . .33  1900 MHz-1920 MHz  1900 MHz-1920 MHzTDD34  2010 MHz-2025 MHz  2010 MHz-2025 MHzTDD35  1850 MHz-1910 MHz  1850 MHz-1910 MHzTDD36  1930 MHz-1990 MHz  1930 MHz-1990 MHzTDD37  1910 MHz-1930 MHz  1910 MHz-1930 MHzTDD38  2570 MHz-2620 MHz  2570 MHz-2620 MHzTDD39  1880 MHz-1920 MHz  1880 MHz-1920 MHzTDD40  2300 MHz-2400 MHz  2300 MHz-2400 MHzTDD41  2496 MHz-2690 MHz  2496 MHz-2690 MHzTDD42  3400 MHz-3600 MHz  3400 MHz-3600 MHzTDD43  3600 MHz-3800 MHz  3600 MHz-3800 MHzTDDNOTE 1:Band 6 is not applicable
In 3GPP, several frequency bands have been specified for different technologies: GSM/GERAN [see e.g. reference 8], UTRAN FDD [see e.g. references 2-3], UTRAN TDD [see e.g. references 4-5], LTE FDD (E-UTRAN FDD) [see e.g. references 6-7] and LTE TDD (E-UTRAN TDD) [see e.g. references 6-7]. The currently standardized LTE FDD and TDD frequency bands are shown in Table 3.
Carrier frequencies in a frequency band are enumerated. The enumeration is generally standardized such that a particular combination of a frequency band and carrier frequency can be determined by a unique number called absolute radio frequency number. In GSM/GERAN, UTRAN and E-UTRAN, the channel numbers are respectively referred to as ARFCN (Absolute Radio Frequency Channel Number), UARFCN and EARFCN.
In FDD systems, separate channel numbers are specified for UL and DL. In TDD there is only one channel number since the same carrier is used in both directions.
The channel number for each band is sufficiently unique to enable different bands to be distinguished. The channel number for a band can be derived from expressions and mapping tables defined in the relevant specifications for each technology. Based on the signaled channel number (e.g., EARFCN) and predefined parameters associated with each band, the UE can determine the actual carrier frequency and the corresponding frequency band. For example the relation between the EARFCN and a DL carrier frequency FDL in MHz (megahertz) is predefined in LTE by the following equation in [see e.g. references 6-7]:FDL=FDL_low+0.1(NDL−NOffs−DL)  (1)where FDL_row (base DL carrier frequency in MHz) and Noffs−DL (base channel number) are predefined values in references 3-4, respectively, for each band, and NDL is the DL EARFCN (DL channel number).
As an illustration, consider the E-UTRA band 5, whose EARFCN NDL as predefined in references 6-7, respectively, lies between 2400-2649. The predefined values of FDL_low and Noff-DL are 869 and 2400 respectively. Assume that the network signals NDL=2500 as the DL channel number. Using the above equation (1), the UE can determine that the DL carrier frequency FDL of the channel is 879 MHz. As indicated above, the predefined EARFNC range is unique for each band. Hence, the UE can determine the frequency band corresponding to the signaled EARFNC. An expression to derive the E-UTRA FDD UL carrier frequency, which is similar to that of the DL carrier frequency, is also predefined.
In E-UTRA FDD, both fixed transmit-receive frequency separation (e.g., fixed duplex) and variable transmit-receive frequency separation (variable duplex) are supported. If a network uses fixed duplex for a DL carrier, then the network only needs to signal the channel number corresponding to the band, i.e., only the DL EARFCN needs to be signaled, since the UE can determine the UL carrier from the DL carrier (from equation (1)) and the predefined duplex gaps in references 6-7. On the other hand, if the network uses variable duplex, it should signal both DL and UL channel numbers, i.e., signal both DL and UL EARFCNs to the UE.
The frequency bands specified in 3GPP or in other standardization organizations may allow cellular manufacturers to build terminal and network products. However, it is generally up to the regional or even country wide regulatory or any relevant authority to decide whether a certain frequency band is allowed or not in their jurisdiction.
Generally, a particular frequency band or spectrum is split into multiple chunks, and in turn the multiple chunks are assigned to multiple operators in a country, region, province, etc by the relevant frequency allocation authority, or similar. A band may also be operator specific in which case it is entirely owned by one operator. An operator specific band is more common when the pass band (i.e., available spectrum) is small or comparable to channel bandwidth or typically channel bandwidth of a technology. But in most cases, a band is divided among multiple operators. An example allocation of a TDD frequency band to different operators is illustrated FIG. 3A.
But as shown in FIG. 3B, a practical deployment comprising of unsynchronized TDD carriers belonging to different operators generally requires a guard band and/or restricted block (e.g., 5 MHz) between at least adjacent carriers to mitigate interference issues. For purposes of this disclosure, the expressions guard band and restricted block may be used interchangeably unless explicitly indicated otherwise. Generally, transmissions on the guard band are not allowed or allowed only under severe restrictions such as transmission with very low power. For the purposes of this document, it may be assumed that little to no meaningful transmission occurs on the guard bands.
In an unsynchronized TDD system, different carriers have arbitrary frame start timings and/or different TDD configurations. Note that FDD frequency band can also be divided among operators as shown in FIG. 4.
Since a band of frequency can generally be used for more than one technology, the band can potentially be also split for different technologies, and the split can vary from one region to another. For instance, the UTRAN FDD band 1 and E-UTRAN FDD band 1 are generally considered to be relatively universal as they are widely available and allocated in a relatively large number of countries across the globe. But they can also be shared among different technologies, and the actual split across technologies can vary.
In USA, the Federal Communications Commissions (FCC) is responsible for attributing licenses for various Wireless Communications Service (WCS) including fixed, mobile, radiolocation or satellite services. Similarly in Europe, the Electronic Communications Committee (ECC), which is part of the European conference of postal and telecommunications administrations (CEPT), is responsible for radio communications. More specifically European Radiocommunications Office (ERO) supports ECC in developing and maintaining the frequency allocation for CEPT member countries. As of today, there are 48 CEPT member countries. Ultimately, each member country has its own frequency allocation. However, the ERO allocation table is used as the basis for developing national frequency allocation. Similar regional organizations are active in other parts of the world for allocating frequencies in their region for different technologies to different operators.
In summary, the actual frequency bands used in a particular region or a country are generally regulated by regional or country wide organizations responsible for frequency allocation in their respective regions.
Multi-Carrier or Carrier Aggregation
It is generally known that in order to enhance peak rates within a technology, multi-carrier or carrier aggregation (CA) can be used. For example, it is possible to use multiple 5 MHz carriers in HSPA (High Speed Packet Access) to enhance the peak rate within the HSPA network. Similarly in LTE, multiple 20 MHz carriers or even smaller carriers (e.g., 5 MHz) can be aggregated in the UL and/or in the DL. Each carrier in the multi-carrier or carrier aggregation system is generally termed as a component carrier (CC) and is also sometimes referred to a cell. A component carrier (CC) may be viewed as an individual carrier in a multi-carrier system.
The term carrier aggregation can be interchangeably called “multi-carrier system”, “multi-cell operation”, “multi-carrier operation”, “multi-carrier transmission” and/or “multi-carrier reception”. CA can be used for transmission of signaling and data in the UL and/or the DL directions.
One CC of the CA is the primary component carrier (PCC) and may also be referred to as the primary carrier or anchor carrier. Each of the remaining CCs is a secondary component carrier (SCC), and may also be referred to as a secondary carrier or supplementary carrier. Generally, the PCC carries the essential UE specific signaling and exists in both UL and DL directions in CA. In case there is single UL CC, the UE specific signaling is on that CC. The network may assign different primary carriers to different UEs operating in the same sector or cell.
Therefore, a UE can have more than one serving cell in DL and/or in the UL: one primary serving cell operating on the PCC and one or more secondary serving cells operating on one or more SCCs. The primary serving cell (PSC) can be interchangeably referred to as the primary cell (PCell). Similarly, each secondary serving cell (SSC) can be interchangeably referred to as the secondary cell (SCell). Regardless of the terminology, the PCell and SCell(s) enable the UE to receive and/or transmit data. More specifically, the PCell and SCell exist in DL and UL for the reception and transmission of data by the UE. The remaining non-serving cells on the PCC and SCC are called neighbor cells.
The CCs belonging to the CA may belong to the same frequency band (intra band CA), to different frequency bands (inter-band CA), or any combination thereof (e.g., 2 CCs in band A and 1 CC in band B). An inter-band CA that includes carriers distributed over two bands is also called as dual-band-dual-carrier-HSDPA (DB-DC-HSDPA) in HSPA or inter-band CA in LTE. The CCs of an intra-band CA may be adjacent (intra-band adjacent CA) or non-adjacent (intra-band non-adjacent CA) in the frequency domain. A hybrid CA that includes any combination of intra-band adjacent, intra-band non-adjacent and inter-band CCs is also possible.
Using carrier aggregation between carriers of different technologies is possible. For example, the carriers from WCDMA and LTE may be aggregated. Another example is the aggregation of LTE and CDMA2000 carriers. Such carrier aggregation can be interchangeably referred to as “multi-RAT carrier aggregation”, “multi-RAT-multi-carrier system” or simply “inter-RAT carrier aggregation”. For the sake of clarity, carrier aggregation within the same technology as described can be regarded as “intra-RAT” or “single RAT” carrier aggregation.
The multi-carrier operation may also be used in conjunction with multi-antenna transmission such as MIMO (multiple-input-multiple-output). For example, signals on each CC may be transmitted by the eNB to the UE over two or more antennas.
The CCs in CA may or may not be co-located at the same site or base station or radio network node (e.g., relay node, mobile relay node, etc). For instance the CCs may originate (i.e., transmitted/received) at different locations (e.g., from non-co-located BS or from BS and RRH or RRU). Examples of combined CA and multi-point communication are DAS, radio remote head (RRH), radio remote unit (RRU), coordinated multipoint transmission and reception (CoMP), and the like. The subject matter described later in this disclosure is applicable to multi-point carrier aggregation systems, i.e., is applicable to each CC in CA or in CA combination with CoMP, and so on.
Random Access (RA)
Random access procedure in LTE enables a UE to gain UL access at least under the following scenarios:                During an initial access in idle mode;        To access a target cell during cell change:                    During a handover;            For a RRC (radio resource control) connection re-establishment such as after radio link failure, and handover failure among others;            For RRC connection release with redirection;                        After the UE has lost the UL synchronization;        Due to data arrival when the UE in a connected mode does not retain UL synchronization such as in a long DRX (discontinuous reception);        To facilitate positioning measurements such as an eNB Rx-Tx time difference measurement, which in turn is used for deriving a timing advance;        To access a SCell (secondary cell) when the UE is configured with at least one SCell.        
The random access procedure can be either contention based or non-contention based. In contention based RA:                The UE randomly selects a ‘random access preamble’ during a RACH (random access channel) opportunity to the eNB;        The network responds to the UE with at least a RA preamble identifier and an initial UL grant in a RAR (random access response) message;        The UE uses the initial allocation received in the RAR to transmit further details related to the connection in a message 3 (msg3). The UE also sends its identifier in the message 3;        The eNB echoes the UE identifier in a CRM (contention resolution message).        
The contention resolution is considered successful if the UE detects its own identity in the contention resolution message. The contention based RA is used only on a PCell (primary serving cell).
The non-contention based RA is normally initiated by the network. In the non-contention based RA:                The network sends the RA preamble, also referred to as a dedicated preamble, to the UE. Thus, there is no contention resolution phase;        The UE sends the assigned preamble during the RACH opportunity to the eNB;        The network responds to the UE with at least a RA preamble identifier and an initial UL grant in the RAR message.        
The UE uses the initial allocation received in the RAR message to transmit further details related to a procedure such as cell change. The contention based RA is also used on the PCell. In case of CA, only non-contention based RA is possible on the SCell.
Self Organizing Network
Advanced technologies such as E-UTRAN and UTRAN may employ the concept of self organizing network (SON). The objective of a SON entity is to allow operators to automatically plan and tune the network parameters and configure the network nodes.
Typically, tuning is performed manually, which may consume an enormous amount of time, resources and which may require considerable involvement of work force. In particular due to the network complexity, large number of system parameters, IRAT technologies, etc., it is very attractive to have reliable schemes and mechanisms that can automatically configure the network whenever necessary. This can be realized by a SON, which can be visualized as a set of algorithms and protocols performing the task of automatic network tuning and configuration. To perform automatic tuning and configuration, the SON node generally requires measurement reports and results from other nodes such as the UE and the base station. The SON can also be used for automatically changing the state of cells from active to idle or vice versa.
UE Timing Control
As seen in FIG. 5, there is a predefined relation between the UL-DL frame timing in LTE. The transmission of a UL radio frame number i from the UE starts (NTA+NTA offset)×TS seconds before the start of a corresponding DL radio frame at the UE, where 0≦NTA≦20512 and NTA offset=624 for frame structure type 2 (LTE TDD).
However, due to the drift in the DL transmission timing and also due to UE mobility, the relation between the UL and DL timing generally needs to be preserved. Therefore, the UE UL transmission and DL reception timings may be controlled and managed by a set of predefined rules, predefined requirements and signaling as described below.
In a cell in LTE, different UEs may be located at different locations in a cell. Also the UEs may be located in a very large cell, e.g., cell range up to 100 km (kilometers). In this case, the signals from different UEs in the cell may be received at the serving radio node (e.g., serving eNB) at different times.
However, in order to ensure orthogonality of the signals received in UL at the receiver of the radio node, transmissions from multiple UEs in the cell generally need to be time aligned. This means the transmit timing of the UEs, which are generally under the control of the same eNB, are adjusted to ensure that their received signals arrived at the eNB receiver at the same time or at least within a fraction of a cyclic prefix (CP). This ensures that the eNB receiver is able to use the same resources (same DFT or FFT resource) to receive and process the signals from multiple UEs. This is achieved by sending timing advanced (TA) commands to the UE such as every 500 ms. The UE then adjust its transmission timing (e.g., increase or decrease) depending upon the TA value.
In CA with two or more UL carriers, multiple TA groups (TAG) can be configured by the network. In this case, the TA may be applied independently on each TAG. Each TAG contains at least one serving cell. At least one TAG includes a primary serving cell and each remaining TAG includes at least one secondary serving cell.
In addition to the TA based adjustment of the UL transmit timing, there is also predefined requirement on the UE to autonomously adjust its UL timing in response to the drift in the eNB transmit timing. More specifically, the UE is generally required to follow the change in the frame transmit timing of the serving cell and correspondingly adjust its transmission timing for each transmission. The UE typically uses signals such as a CRS (common reference signal) and synchronization signals to track the DL timing of the serving cell.
The serving cell timing may change due to different reasons including variation in radio conditions, clock imperfections, maintenance activities, and deliberate attempt by the network to change timing among others. Generally, it is also required that the UE changes its UL transmit timing (increase or decrease) with a certain predefined slew rate. This is to ensure that the UE does not change the timing too fast. This requirement stems from the fact that if the UE changes its UL transmit timing in the order of several μs from subframe to subframe, the base station receiver may not be able to cope with the received signals. This may result in degradation of demodulation of signals transmitted by the UE. Typically the eNB receiver can handle with some acceptable performance degradation, the UE received signal whose transmission timing has been changed up to 1-2 μs in a single transmission. However, if the UE changes its transmission timing in the order of 3 μs or more, the receiver at the radio node may not be able to receive or demodulate the UE received signal.
The predefined rules and requirements governing the UL timing adjustments with predefined slew rates depend upon the BW and can include:                A maximum magnitude of the UL timing change in one adjustment step as T1, e.g., 100 ns for 5 MHz BW;        A minimum aggregate UL timing adjustment rate as T2 over certain of time, e.g., 300 ns per second for 5 MHz BW;        A maximum aggregate UL timing adjustment rate as T3 over certain period of time, e.g., 1 μs per 200 ms for 5 MHz BW.        
If the UE receives the TA command from the network while autonomously changing the UL timing, then it may stop the autonomous adjustment and instead applies the TA command to change its timing.
In CA, multiple TA groups are configured by the network, and the UE may independently adjust its UL timing on each set of serving cells in a TAG. In this case, the UE uses PCell as the DL timing references for the TAG containing the PCell, and uses the SCell as the DL timing reference for the TAG containing SCell for adjusting its UL transmit timings on each TAG.
Measurements
The measurements are performed by the UE and/or the radio node. Theses are described below:
Cell identification or cell search may also be considered a type measurement. When a UE is powered on, it first searches cells on possible frequencies (or channels) in a frequency band. A multi-RAT multi-band UE searches all its supported bands for each supported RAT unless explicitly forbidden. The UE attempts to find the most suitable frequency channel in a particular band in use in that region. The UE then proceeds with remaining tasks or more specifically may acquire the cell timing and cell ID of neighbor cells, which are operated on the same frequency channel found in the first step. The process of searching frequency channel is often called as the initial cell search. Terms such as band scanning and frequency search are also commonly used for the initial cell search in literature.
After acquiring frequency synchronization, the UE may acquire system information of the detected cell found during the initial cell search, and acquire information about neighbor cells. The UE typically uses the neighbor cell information (e.g., neighbor cell list) to start a neighbor cell search. The UE then continuously attempts to find the cell timing and physical ID (identification) of the cells operating on the acquired carrier frequency. Once the UE camps on the strongest (e.g. best, or most suitable) cell, the broadcast information is downloaded and the location area update in UMTS or tracking area update in LTE is carried out. If authentication fails, the UE attempts to connect to another suitable cell or to a cell of another allowed PLMN.
The UE may perform measurements on the serving and on the neighbor cells over some known reference symbols or pilot sequences. The measurements may be performed on cells on an intra-frequency carrier(s), inter-frequency carrier(s), and inter-RAT carriers(s) depending upon whether (or not) the UE is capable of supporting that RAT.
The UE may receive measurement configuration or an assistance data and/or information, which is a message or an information element (IE) sent by the network node (e.g., serving eNB, positioning node, etc.) to configure the UE to perform requested measurements. For example the message or the IE may contain information related to the carrier frequency, RATs, types of measurement (e.g., RSRP), higher layer time domain filtering, measurement bandwidth related parameters, and so on.
Some measurements may also require the UE to measure signals transmitted by the UE in the UL. The measurements are performed by the UE in RRC connected state and in low activity RRC states (e.g., idle state, CELL_FACH state in HSPA, URA_PCH and CELL_PCH states in HSPA). In multi-carrier or CA scenario, the UE may perform the measurements on the cells on the primary component carrier (PCC) and on the cells on one or more secondary component carriers (SCCs).
The measurements may serve various purposes. Some example purposes may include: mobility, positioning, self organizing network (SON), minimization of drive tests (MDT), operation and maintenance (O&M), network planning and optimization, etc.
The measurements are typically performed over a relatively long time duration in the order of few 100 ms to few seconds. The same measurements are applicable in single carrier and in CA. However, in CA, the measurement requirements may be different. For example the measurement period may be relaxed or made more stringent in CA depending upon whether or not the SCC is activated or not. This may also depend upon the UE capability i.e., whether or not a CA capable UE is able to perform measurement on SCC with or without gaps.
Examples of mobility measurements:                in LTE include:                    Reference symbol received power (RSRP);            Reference symbol received quality (RSRQ);                        in HSPA include:                    Common pilot channel received signal code power (CPICH RSCP);            CPICH Ec/No;                        in GSM/GERAN includes GSM carrier RSSI;        in CDMA2000 systems include:                    Pilot strength for CDMA2000 1xRTT;            Pilot strength for HRPD.                        
The mobility measurement may also include identifying or detecting a cell, which may belong to LTE, HSPA, CDMA2000, GSM, etc. Identification of a cell by the UE may comprise at least acquiring a cell identifier of a cell. The cell identifier can be a PCI, CGI or any type of identifier which denotes the cell.
Examples of positioning UE measurements in LTE include:                Reference signal time difference (RSTD);        UE RX-TX time difference measurement. This measurement requires the UE to perform measurement on the DL reference signal as well as on the UL transmitted signals.        
Example of other measurements which may be used for MDT, SON or for other purposes include:                Control channel failure rate or quality estimate:                    Control channel failure rate:                            Paging channel failure rate;                Broadcast channel failure rate;                                    Random access failure:                            Number of random access (RA) failures over a time period;                Percentage or fraction of RA failure, i.e., ratio of RA failures to RA attempts;                                                Physical layer problem detection:                    Radio link monitoring (RLM), which includes:                            Out of synchronization (out of sync) detection;                In synchronization (in-sync) detection;                                    Radio link failure (RLF).                        
The UE may also perform measurements on the serving cell (primary cell) in order to monitor the serving cell's performance. This is referred to as radio link monitoring (RLM) or RLM related measurements in LTE. For RLM, the UE monitors the DL link quality based on the cell-specific reference signal in order to detect the DL radio link quality of the PCell.
To detect out of sync and in sync, the UE compares the estimated quality with the thresholds Qout and Qin, respectively. The thresholds Qout and Qin are defined as a level at which the DL radio link cannot be reliably received and corresponds to 10% and 2% BER (block error rate) of a hypothetical PDCCH (physical dedicated control channel) transmissions, respectively.
In non-DRX, the DL link quality for out of sync and in sync are estimated over an evaluation periods of 200 ms and 100 ms respectively.
In DRX, the DL link quality for out of sync and in sync are estimated over the same evaluation period, which scale with the DRX cycle e.g., period equal to 20 DRX cycles for DRX cycle greater than 10 ms and up to 40 ms.
When in the connected state, the UE reports the neighbor cell measurements to the serving node. The measurement reporting can be performed by one or more mechanisms depending upon various considerations including, among others, the type of measurement and the network configuration. Examples of measurement reporting mechanism include periodic reporting, event triggered reporting, one shot reporting upon explicit network request, event triggered periodic reporting, and reporting of logged measurements when certain condition is met (e.g., logging timer expires, buffer size is above threshold).
In response to the reported UE measurement, the serving node can make a determination related to whether to perform a radio operational task or a radio resource management action. For example, the serving node may send mobility command to the UE for the purpose of cell change, modify one or more parameters, and so on. Examples of cell change include handover, RRC connection re-establishment, RRC connection release with redirection, PCell change in CA, and PCC change in PCC.
In idle state or low activity state, the UE does not report the measurements to the network. Rather, it autonomously uses one or more measurements for radio operational task or radio resource management action such as cell change and modification of radio related parameters (e.g., measurement rate or intensity of doing measurement). Examples of cell change in idle state or low activity state include cell selection and cell reselection.
A legacy single carrier UE (i.e., non CA capable) typically has a receiver that is able to receive data only on one carrier frequency (e.g., 5 MHz in WCDMA, up to 20 MHz in LTE. Note that one carrier in LTE can be up to 20 MHz. This means that such a UE needs measurement gaps to perform inter-frequency and inter-RAT measurements.
The measurements may belong to any category. For example they may be neighbor cell measurements (e.g., PCI identification in LTE or HSPA; ECGI or CGI identification in LTE FDD/TDD; HSPA FDD/TDD, LTE RSRP or RSRQ measurements in LTE; CPICH RSCP, CPICH Ec/No measurements in WCDMA). Other examples include: GSM carrier RSSI measurement, GSM BSIC identification, CDMA2000 measurements (e.g., CDMA 2000 1x Pilot Strength, HRPD Pilot Strength).
There may also be positioning related measurements such as RSTD in LTE. The UE may also be able to perform other types of measurements including measurements for minimization of drive tests such as pilot measurements or BCH failure rate, and measurements for self organizing network (SON).
During the measurement gaps, the UE performs measurement on the target frequency or target RAT and therefore it cannot receive the data from the serving cell. There are basically two types of gaps for performing measurements:                Network configurable measurement gaps. Examples include compressed mode gaps in HSPA and measurement gaps in LTE;        UE autonomous gaps including gaps autonomously created by the UE when the UE is requested to read system information of a neighbor cell.        
In WCDMA, the measurement gaps are referred to as “compressed mode (CM) patterns”. The CM pattern comprises periodical gaps of 7 or more slots occurring with certain periodicity. During the gaps, the UE switches from the serving WCDMA carrier to the WCDMA inter-frequency or inter-RAT frequency (e.g., to LTE carrier) to perform the measurement on the target inter-frequency or inter-RAT frequency.
In WCDMA, a separate CM pattern is to be activated to perform the measurement on each inter-frequency or inter-RAT carrier. The CM patterns allow the UE, at least to some extent, to recover the data lost during the gaps e.g., by lowering the spreading factor and increasing the BS transmitted power to the UE during the recovery frames.
In LTE, the inter-frequency and inter-RAT measurements are also performed during periodical gaps, which occur with periodicity of 40 ms (pattern #0) or 80 ms (pattern #1). Each gap during which the UE performs inter-frequency and inter-RAT measurements is 6 ms. Unlike WCDMA, the loss in data during the LTE gaps cannot be compensated. This is because there is no concept of compressed frames and/or sub-frames. This means in LTE, the peak data rate may be reduced due to the measurement gaps, where data cannot be transmitted.
In HSPA and LTE, the serving cell can request the UE to acquire the system information (SI) of the target cell. More specifically the UE reads the SI to acquire the cell global identifier (CGI), which uniquely identifies the target cell.
The UE may read the SI of the target cell (e.g., intra-frequency, inter-frequency, inter-RAT cell) upon receiving an explicit request from the serving network node, e.g., RNC in HSPA or eNB in LTE, via RRC signaling. The acquired SI is then reported to the serving cell. The signaling messages are defined in the relevant HSPA and LTE specifications.
To acquire the SI which contains the CGI of the target cell, the UE reads at least part of the SI including master information block (MIB) and the relevant system information block (SIB) as described later. Terms SI reading/decoding/acquisition, CGI/ECGI reading/decoding/acquisition, CSG SI reading/decoding/acquisition may be interchangeably used herein to have same or similar meaning.
The reading of SI for the acquisition of CGI is carried out during measurement gaps which are autonomously created by the UE. The number of gaps and their size may thus depend upon UE implementation as well as on other factors including radio conditions and type of SI to be read. The term autonomous indicates that the network does not know exactly when the gaps are created. The gaps may be created at least in the DL, in which case the UE cannot receive data. Autonomous gaps may also be created in the UL, especially when acquiring the SI of the target inter-frequency cell or inter-RAT cell. In this case, the UE can neither receive nor transmit data.
In contrast, normal periodical measurement gaps (aka compressed mode pattern, transmission gaps, etc) are used to perform, for instance mobility measurements such as RSRP and RSRQ. They are configured by the network by sending explicit configuration to the UE. Hence, in this case, the network may precisely know the location in time of each gap.
Autonomous gaps are generally needed since the UE cannot receive and/or transmit data in parallel with the reading of the SI of a target cell. The reason is that the simultaneous operation may increase complexity, memory requirements and power consumption. Furthermore, a legacy single carrier UE (non CA capable) typically has a single receiver for receiving data only on one carrier frequency, e.g., 5 MHz BW (bandwidth) in WCDMA or up to 20 MHz BW in LTE (note that a single carrier in LTE can be up to 20 MHz wide). This means that the legacy UE may need autonomous gaps to acquire at least the inter-frequency and inter-RAT SI. The SI reading may also be used for acquiring additional information such as CSG and/or hybrid CSG indicators.
In LTE, the UE reads the MIB and SIB1 (SystemInformationBlockType1) of the target E-UTRAN cell (which can be FDD or TDD) to acquire its cell global identifier—the ECGI—when the target cell is E-UTRAN intra- or inter-frequency cell. The MIB is transmitted periodically with a periodicity of 40 ms and repetitions made within 40 ms. The first transmission of the MIB is scheduled in subframe 0 of radio frames for which the SFN mod 4=0, and repetitions are scheduled in subframe 0 of all other radio frames. The MIB may comprise basic information such as cell bandwidth and SFN.
The LTE SIB1, as well as other SIB messages, may be transmitted on DL-SCH (downlink shared channel). The SIB1 may be transmitted with a periodicity of 80 ms and repetitions made within 80 ms. The first transmission of the SIB1 may be scheduled in subframe #5 of radio frames for which the SFN mod 8=0, and repetitions may be scheduled in subframe #5 of all other radio frames for which SFN mod 2=0. The LTE SIB1 may also indicate whether a change has occurred in the SI messages. The UE may be notified about a coming change in the SI by a paging message, from which it will know that the SI will change at the next modification period boundary. The modification period boundaries may be defined by SFN values for which SFN mod m=0, where m is the number of radio frames comprising the modification period. The modification period may be configured by system information. The SIB1 contains information such as CGI, CSG identity, frequency band indicator, etc.
In HSPA, the UE reads the MIB and SIB3 of the target cell UTRAN cell to acquire its CGI (aka Neighbor Cell SI) when the target cell is a UTRAN intra-frequency or inter-frequency cell [2]. The MIB provides basic information such as SFN and SIB3 contains the CGI of the target cell.
The procedure for inter-RAT SI acquisition during autonomous gaps may also be specified for inter-RAT UTRAN, inter-RAT E-UTRAN, inter-RAT GEM/GERAN, inter-RAT CDMA2000 among others:                In case of inter-RAT UTRAN, the UE served by the E-UTRAN cell reads the MIB and SIB3 of the target UTRAN cell during the autonomous gaps to acquire the UTRAN cell SI such as the UTRA cell CGI;        In case of inter-RAT E-UTRAN, the UE served by the UTRAN cell reads the MIB and SIB1 of the target E-UTRAN cell (which can be FDD or TDD) during the autonomous gaps to acquire E-UTRAN cell SI such as the E-UTRA cell CGI;        In case of inter-RAT CDMA2000, the UE served by the E-UTRAN cell reads the relevant broadcast information of the target CDM2000 cell to acquire CDM2000 cell SI such as the CDMA2000 cell CGI. CDMA2000 is a generic term. The target CDMA2000 cell can belong to CDMA2000 1x RTT or HRPD systems.        
The target cell whose SI can be acquired can be an intra-frequency cell, an inter-frequency cell or an inter-RAT cell (e.g., UTRAN, GERAN, CDMA2000 or HRPD). There are at least few well known scenarios for which the serving cell may request the UE to report the CGI of the target cell:                Verification of CSG cell;        Establishment of SON ANR (automatic neighbor relation);        MDT (minimization of drive tests).        
The UE also performs and report channel state information (CSI) measurements to the network node to facilitate among others scheduling, link adaptation, and antenna mode selection among others. In LTE, CSI measurements include:                RI (rank indication)—indicates recommended number of layers for DL transmission using DL multi antenna scheme;        PMI (precoder matrix indication)—indicates recommended precoder matrix to be used for the DL transmission;        CQI (channel quality indication)—indicates the highest MCS (modulation and coding) scheme or transport format that can be used for DL transmission.        
The CSI measurements and reporting are configured at the UE by its serving node. In LTE, the network node (e.g., eNB) can configure the UE to report the CSI using periodic and/or aperiodic mechanisms.
The measurements are also performed by a radio node on signals related to a UE. The measurement can be performed on signals transmitted by a UE and/or on signals transmitted by the radio node to a UE. Examples of radio nodes include, among others, base stations, NodeBs, eNBs, base transceiver stations (BTS), relays, measuring nodes (e.g., location measurement unit (LMU)).
Examples of UTRAN measurements, which are defined in 3GPP Technical Specifications TS 25.215 and TS 25.225, include received total wide band power, signal to interference radio (SIR), SIR error, transmitted carrier power, transmitted code power, transport channel BER, physical channel BER, RTT (round trip time), acknowledged PRACH preambles, SFN-SFN observed time difference, Angle of Arrival (AoA), UTRAN GPS Timing of Cell Frames for UE positioning, UTRAN GANSS Timing of Cell Frames for UE positioning, etc.
Examples of E-UTRAN measurements, which are defined in TS 36.214, include DL RS TX power, RIP (received interference power), thermal noise power, timing advance (TADV), eNB Rx-Tx time difference, E-UTRAN GNSS Timing of Cell Frames for UE positioning, Angle of Arrival (AoA), UL Relative Time of Arrival (RTOA) for UTDOA positioning, etc.
The overall serving cell or neighbour cell measurement quantity results may comprise of non-coherent averaging of 2 or more basic non-coherent averaged samples. The exact sampling depends upon the implementation and is generally not specified. An example of RSRP measurement averaging in E-UTRAN is shown in FIG. 6. The figure illustrates that the UE may obtain the overall measurement quantity result by collecting four non-coherent averaged samples or snapshots (each of 3 ms length in this example) during the physical layer measurement period (i.e., 200 ms) when no DRX is used or when DRX cycle is not larger than 40 ms. Every coherent averaged sample is 1 ms long. The measurement accuracy of the neighbour cell measurement quantity (e.g., RSRP or RSRQ) is specified over this physical layer measurement period. It should be noted that the sampling rate is generally UE implementation specific. Therefore, in another implementation a UE may use only 3 snap shots over 200 ms interval. Regardless of the sampling rate, it is important that the measured quantity fulfils the performance requirements in terms of the specified measurement accuracy.
In case of RSRQ, both RSRP (numerator) and carrier RSSI (denominator) should be sampled at the same time to follow similar fading profile on both components. The sampling also depends upon the length of the DRX cycle. For example for DRX cycle>40 ms, the UE typically takes one sample every DRX cycle over the measurement period.
A similar measurement sampling mechanism may be used for other signal measurements by the UE and also by the BS for UL measurements.
In-Device Coexistence Involving External Wireless Systems
A cellular UE can be equipped with external wireless system, i.e., non-cellular, communication systems. Examples of such external wireless systems which can be located on a cellular device or UE include LTE, WiFi, Bluetooth transceivers, Global Navigation Satellite System (GNSS) receiver, sports or medical related short range wireless devices, medical gadgets, cordless telephones, etc. Examples of GNSS include GPS, Galileo, COMPASS, and GANSS. The transmit power of one or more transmitters (e.g., LTE) may be much higher than which can be managed by a receiver of another system (e.g., WLAN). In particular, due to extreme proximity of these radio transceivers in the same device, the impact of the aggressor system's interference on a victim radio receiver can be severe. One example of in-device co-existence is the LTE TDD band 40 and ISM band (2.4 GHz). Another example is the HSPA/LTE FDD band VII/7 and ISM band (2.4 GHz).
There are known ways to mitigate interference in the in-device co-existence scenario (i.e., between cellular systems and in-device external wireless systems). For example, the network can allow the UE to autonomously create gaps on cellular systems when the external wireless system (e.g., WLAN) is accessed. The network can also perform inter-frequency handover to avoid interference. The network can also configure the UE in a long DRX cycle, and during the DRX OFF duration the UE can use the external wireless systems. The network can also configure the UE with a pattern of subframes (e.g., repeated every 40 ms or subframes) to partition the time to be shared between the cellular system (e.g., LTE band 40) and external wireless systems (e.g., WLAN).
Multi-SIM Operation
The subscriber identity module (SIM) may contain subscriber related information such as the subscriber's PLMN ID, supported RATs by an operator, etc. A public land mobile network (PLMN) is a set of an access network, core network and other necessary mobile network elements or entities forming a complete mobile network. A SIM (i.e., formerly for only GSM) or USIM (i.e., for UMTS, LTE or even GSM/UMTS/LTE) card may be interchangeably used. For consistency, the term SIM will be used to encompass USIM or any type of SIM regardless of supported technologies and/or RATs.
A UE may include capabilities to establish two or more cellular communication operations with different PLMNs in parallel. This may be realized through a multi-SIM operation in a UE, and such a UE is termed as a multi-SIM capable UE. The PLMNs involved in the multi-SIM operation typically belong to different operators, but they may also belong to the same operator. In both cases, all supported SIMs are typically associated with independent subscriptions.
Different SIMs may operate using the same technology and/or RAT or different technologies and/or RATs at the same time. Some of the existing UE implementations generally support dual SIM operation in which two SIMs can operate simultaneously. For example, the dual SIMs of the UE may support GSM/UTRAN FDD and LTE. As another example, the SIMs may simultaneously operate on different LTE carriers belonging to different operators' PLMNs. In yet another example, the dual SIMs may operate simultaneously on LTE and HSPA carriers belonging to different operators' PLMNs.
The underlying radio technology used for realizing the multi-SIM operation may be through a single radio, through multiple radios, or even through a broad band radio. In single radio case, one SIM may be used for radio communication at a time; however, the UE may perform measurements or may receive paging or other messages on the other SIMs which can cause periodic or sporadic interruptions on communication related to the first SIM. In multi-radio operation, two or more SIMs can establish simultaneous radio communications. A broadband radio may also support also simultaneous radio communications provided that the carriers are within the supported bandwidth of the broadband radio. The multi-radio or the broadband multi-SIM operation is similar to multi-carrier operation.
An advantage of the multi-radio or the broadband multi-SIM operation is that it enables full simultaneous radio communication with different PLMNs. It also prevents the need for interruptions or gaps for measurements and/or paging on carriers used by other SIMs. A drawback of multi-radio or broadband multi-SIM operation is that the simultaneous radio communications belonging to different PLMNs may cause the out of band emissions (e.g., due to leakage, harmonics, etc) from one carrier pouring into the receiver of another carrier and vice versa degrading the performance.
Heterogeneous Network
In order to mitigate interference in heterogeneous networks (e.g., comprising a mix of high power nodes (e.g, a macro BS) and low power nodes (e.g., pico BS)), a time domain enhanced inter-cell interference coordination ICIC (eICIC) has been specified in release 10 for LTE. In this scenario, the high power node may be viewed as an aggressor node and the lower power node may be viewed as a victim node.
According to the time domain eICIC scheme, a time domain pattern of low interference subframes are configured in the aggressor node. The pattern is also referred to as a low interference transmit pattern or an ABS (almost blank subframe) pattern. An ABS pattern is configured in the aggressor cell and/or node to protect resources in subframes in the victim node and/or cell receiving relatively strong inter-cell interference from the aggressor cell. ABS subframes are typically configured with reduced transmit power or no transmission power and/or reduced activity on some of the physical channels.
In an ABS subframe, the basic common physical channels such as CRS, PSS/SSS, PBCH and SIB1 are transmitted to ensure the operation of the legacy UEs. The ABS pattern can also be categorized as non-MBSFN and MBSFN. In a non-MBSFN ABS pattern, an ABS can be configured in any subframe (MBSFN or non-MBSFN configurable subframes). In a MBSFN ABS pattern, an ABS can be configured only in MBSFN configurable subframes (subframes 1, 2, 3, 6, 7 and 8 in FDD and subframes 3, 4, 7, 8, and 9 in TDD).
The serving eNB (e.g., pico eNB) may signal one or more measurement patterns (aka measurement resource restriction pattern) to inform the UE about the resources or subframes which the UE should use for performing measurements on a target victim cell (e.g., serving pico cell and/or neighboring pico cells). The patterns can be different for serving cell measurements and for neighbor cell measurements. The resources or subframes on which the measurements are to be performed by the UE overlap with ABS subframes in the aggressor cell(s). Therefore, these resources or subframes within a measurement pattern are protected from aggressor cell interference and are interchangeably also called protected subframes or restricted subframes. The serving eNB ensures that each measurement pattern contains at least certain number of protected subframes in every radio frame, e.g., one or two, to facilitate UE to perform measurements. Otherwise, the UE would be unable to meet the predefined measurement requirements when configured with measurement patterns related to operation in a heterogeneous network.
A signal transmit pattern or a measurement pattern comprises of a bit map and typically repeats after certain number of frames e.g., every 4 frames or 40 ms for LTE FDD and every 7 frames or 70 ms for LTE TDD.
Positioning Overview
Several positioning methods exist for determining the location of a target device, which can be any of the wireless device or UE, mobile relay node, PDA, etc. The position of the target device is determined by using one or more positioning measurements, which can be performed by a suitable measuring node or device. Depending upon the positioning, the measuring node can either be the target device itself, a separate radio node (i.e., a standalone node), serving and/or neighboring node of the target device among others. Also depending upon the positioning method, the measurements can be performed by one or more types of measuring nodes. Conventional positioning methods include, e.g.:                Satellite based techniques—measurements performed by the target device on signals received from the navigational satellites are used for determining target device's location. For example either GNSS or A-GNSS (e.g., A-GPS, Galileo, COMPASS, GANSS, etc) measurements are used for determining the UE position;        OTDOA—UE measurements related to time difference of arrival of signals from radio nodes (e.g., UE RSTD measurement) are for determining UE position in LTE or SFN-SFN type 2 in HSPA;        UTDOA—measurements performed at a measuring node (e.g., LMU) on signals transmitted by a UE are used for determining the UE position;        Enhanced cell ID—uses one or more of measurements for determining the UE position e.g., any combination of UE Rx-Tx time difference, BS Rx-Tx time difference, timing advanced (TA) measured by the BS, LTE RSRP/RSRQ, HSPA CPICH measurements (CPICH RSCP/Ec/No), angle of arrival (AoA) measured by the BS on UE transmitted signals, etc for determining UE position. The TA measurement is performed using use either UE Rx-Tx time difference or BS Rx-Tx time difference or both;        Hybrid methods—rely upon measurements obtained using more than one positioning methods for determining the UE position.        
In LTE, the positioning node such as a E-SMLC or a location server may configure the UE, eNB or LMU to perform one or more positioning measurements depending upon the positioning method. The positioning measurements are used by the UE, a measuring node and/or by the positioning node to determine the UE location. The positioning node may communicate with a UE using a LPP protocol and with eNB using a LPPa protocol.
Generally, regulators may divide a frequency spectrum or a frequency band available for wireless communication into several blocks of spectrum or frequencies. One or multiple frequency blocks are then assigned, or allocated, to different operators. A small frequency band may also be entirely assigned to a single operator. However, most frequency bands are large enough and are split among multiple operators.
The frequency assignment principle and criteria depend upon the particular regulatory authority. For example, the TDD frequency band 38 (2.6 GHz—see Table 3 above) can be divided into 10 blocks, in which each block is 5 MHz wide. This 50 MHz spectrum can be divided among three operators: 3×5 MHz, 3×5 MHz and 4×5 MHz. If the operators want unsynchronized TDD operation, one drawback may be that each operator will have to sacrifice e.g., 5 MHz of their spectrum to introduce inter-operator guard band and/or restricted block. Another drawback may be that the vendor has to develop customized radio network equipment for each operator.
The operators can use synchronized TDD operation to remove the need to sacrifice a part of their allocated spectrum. However, in order to ensure synchronized TDD operation, the operators may need to coordinate and agree on a common TDD UL and/or DL configuration (i.e., common frame alignment and common TDD UL/DL configuration). However the coordination and determination of the most suitable TDD configuration for all operators using adjacent carriers in the same TDD band may be quite challenging in some scenarios. This may be because the optimum use of a TDD configuration depends upon several factors including type of services, symmetry or distribution between UL and DL traffic, cell size, radio environment, etc.
It may be almost impossible or at least quite challenging to determine a common TDD configuration that can satisfy the demand of all operators due to differences in one more requirements mentioned above. For example an operator which mainly offers data services may require a TDD configuration with larger number of DL subframes compared to UL subframes in a frame. Another operator which mainly offers voice services may require TDD configuration with equal allocation of DL and UL resources (i.e., subframes) in a frame. Yet a third operator may have a very larger number of the subscribers uploading files or sending data. Such operator may require TDD configuration with larger number of UL subframes compared to the DL subframes in a frame. The traffic demand and the types of services used by the subscribers may also change over time. In such scenarios, the coordination among the operators becomes even more complex.
The problem, or challenge, described above is more severe for TDD bands due to cross UL-DL subframe/slot interference, which can be mitigated either by introducing guard band/restricted blocks (see FIG. 3B) or by synchronized operation among operators using adjacent carriers in the same band (see FIG. 3A).
The current LTE TDD co-existence and co-location radio requirements for UE and BS are defined in references 6-7 under the assumption that all TDD carriers are synchronized, i.e., they use the same TDD configuration and are frame synchronized. This means there are no requirements for unsynchronized operation and may lead to severe performance degradation if TDD carriers are not synchronized in practice.
Note that regardless of whether synchronized or unsynchronized operation is used, a peak rate that an operator can provide depends on the amount of spectrum assigned to that operator. In the above example, the peak rates that can be offered by the three operators will be limited due to the peak rate that can be carried on frequency spectrums that are 15 MHz, 15 MHz, and 20 MHz wide, respectively.
The FDD band can also be split among multiple operators (see FIG. 4). The peak data rate offered by an FDD operator also depends upon the amount of the spectrum assigned, or allocated, to that operator. For example, an FDD operator assigned 10 MHz in band 1 (2 GHz—see Table 3) can offer services using LTE channel up to 10 MHz channel. Generally, such operator cannot offer higher data rate using other larger LTE channels such as 15 or 20 MHz channel. Similarly the operator also cannot use intra-band CA to further enhance the bit rate.